Recent findings from this laboratory suggest that the changes that occur in the lung and liver endothelial cells of animals exposed to the pyrrolizidine alkaloids and their metabolites arise as a result of covalent binding of these compounds with cellular components, thus altering or inhibiting their functional role. The covalent binding to the SH groups of glutathione, cysteine and dehydrogenase under in vitro conditions and the preferential binding to proteins of the cell under in vivo conditions implicate an early alteration in the cellular proteins as the primary injury that occurs in the endothelial cells of affected animals. Further research will clarify this point. In these experiments H3 dehydroretronecine, a tertiary metabolite of monocrotaline, and a semi-synthetic pyrrole disenecioyl dehydroretronecine will be evaluated under in vitro and in vivo conditions. The former compound is quite stable and has been shown to be effective in causing pulmonary and hepatic vascular changes in experimental animals. Although the naturally occurring pyrroles are extremely toxic, they are extremely labile and difficult to evaluate. The semi-synthetic pyrrole that has recently been synthesized and tritiated circumvents the difficulties of working with the conventional pyrroles. Preliminary data suggest that the cellular changes produced by this semi-synthetic pyrrole are similar to those caused by monocrotaline pyrrole. The two metabolites of monocrotaline will be exposed to purified macromolecules as well as to endothelial cell cultures to determine the nature of their interaction with cellular components. Identification of the chemical interaction will be determined by chromatography, NMR, IR and mass spectrometry. In addition, in vivo experiments will be conducted to determine the sequential changes that occur in the endothelial cells exposed to these two metabolites. Morphological evaluations will be correlated with electron microscopic autoradiography to determine the association of the lesions that develop with the localization of radioactivity in the affected cells.